An output voltage for a charger specified by an international standard is typically 5±5% V, i.e., 4.74 V-5.25 V. A universal serial bus (USB) wire for connecting a mobile phone to the charger generally has a resistance, usually 0.2Ω for a premium USB wire, and 0.3-0.4Ω for an ordinary one. Thus, in a case in which a charging current is 1 A, a voltage drop across the USB wire will be more than or equal to 0.2 V. In view that there is another voltage drop of about 0.1 V on a printed circuit board (PCB) in the mobile phone, an input voltage to a charging management chip of the mobile phone can be less than 4.7 V. As a result, the voltage actually output from the charger to the charging management chip of the mobile phone may not meet the international standard.
Conventionally, under a charging management chip with an efficiency of 90%, a 4.2 V battery may be charged to 4.2 V in a fast charging phase (the charging current being 1 A). However, a 4.35 V high voltage battery may not be charged to 4.35 V in the fast charging phase because the input voltage to the charging management chip of the mobile phone may not reach about 4.85 V.